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Does a '91 HO engine bolt up to a '90?

ZmOz

NAXJA Forum User
I'm looking for a new 4.0 engine to build a stroker with, and I found one for a really good price. Problem is it's a 91, HO, I was hoping for an 87-90. Will that just bolt right up in my '90? I'm assuming the computer won't like that? Is the block exactly the same?
 
Mechanically, the are pretty much the same with a couple minor changes (in 1991, the knock sensor was deleted, and I think the CTS was removed from the head.) The Renix thermal fan switch is located in the left radiator tank, while the HO has it in the thermostat housing (easy fix - use the old housing or plug the hole in the new.)

You'd probably have to D&T for the knock sensor (which I prefer to retain, I've all but fallen in love with Renix electronics!) but everything else should be okeh.

IIRC, the 4.0 block was pretty much unchanged (as a basic casting) from inception to demise in 2001. I think all they did for DIS was to install a blank to cover the driveshaft for the oil pump, and maybe machine some extra bolt holes in the head for the ignition rail... I've not seen one just yet, tho, so that's just a guess.

5-90
 
So, as far as bolt holes and sensors go, it's exactly the same except the knock sensor and fan thermostat? What about the CPS, isn't that different on the HOs?
 
Everything on the block, bolt holes will match up to the trans. The sensors are where you get into some difference. MAP, TPS, EGR, Temp sensor, open raditator system. The exhaust header is different. Where are you located. I have my old 4.0 block that needs a rebuild for sale in PA. Came out of my 88' XJ. In great shape, just got a really good deal on a rebuilt long block. I was going to make a stroker project out of it for my next XJ. Let me know. Juice
 
juicexj24 said:
Everything on the block, bolt holes will match up to the trans. The sensors are where you get into some difference. MAP, TPS, EGR, Temp sensor, open raditator system. The exhaust header is different. Where are you located. I have my old 4.0 block that needs a rebuild for sale in PA. Came out of my 88' XJ. In great shape, just got a really good deal on a rebuilt long block. I was going to make a stroker project out of it for my next XJ. Let me know. Juice

I'm in Oregon...I might be interested in that block depending on how much you want for it. :) I was already thinking of getting the engine/trans shipped from Alabama.
 
The CPS bolts to the transmission bellhousing, and only needs to be converted if you plan on changing computers (since there is a different type of sensor used on the HO vice the Renix.) No problem there. Also, the fan sensor shouldn't be a problem since it isn't mounted on the engine anyhow.

I forgot to mention - the manifold mounting on the HO head is different from the Renix, some modification is required if you don't keep the old head. The HO head flows better, but a lot of Renix stuff (doesn't quite bolt right up to the HO intake (but it can be modified with a little patience.)

5-90
 
I have a complete (less intake) 91ho that would be the perfect candidate for a stroker project. Ran when I pulled it (200k miles) all I want is $75 plus shipping or stop in if you want.
 
asatxj said:
I have a complete (less intake) 91ho that would be the perfect candidate for a stroker project. Ran when I pulled it (200k miles) all I want is $75 plus shipping or stop in if you want.

Hmm...might be interested...exactly how complete is it? Starter/alt/PS pump/sensors/AC/ect? :)
 
For $75 you are hoping for all that? this is a complete "junkyard motor" plus all the brackets, waterpump, exhaust manifold, distributor etc(oh yeah, I'll give you the flexplate and inspection cover . My bro-in-law just bought a motor with everything(all the stuff you listed) and paid $600. I'm basically giving this thing away because I'm not interested in doing a stroker and it's taking up space in my storage building that I need. Buy the exhaust manifold for $75 get a free motor.
 
No, I wasn't expecting all that for $75. The reason I asked, is because when people say "complete motor" That includes those things...otherwise it isn't complete. ;) I'll let you know by tomarrow if I want it or not...thanks!
 
ZmOz said:
No, I wasn't expecting all that for $75. The reason I asked, is because when people say "complete motor" That includes those things...otherwise it isn't complete. ;) I'll let you know by tomarrow if I want it or not...thanks!

No, that is not correct. A complete engine is a complete engine -- it includes the block, the head, the water pump, the flywheel or flexplate, and maybe the intake and exhaust manifolds (for a used engine, but not for a new long block). A/C compressor, power steering pump, and fuel system are not usually included unless you agree to pay extra for them. Starter is hit-or-miss.
 
only minor differences in the block, like stated before the coolant temperature sending unit is located on the tstat housing not the block, (on pre high output they are on the drivers side next to the engine drain plug) and the oil filter housing uses the new pattern 51085 wix filter number (you can switch the housing but why bother just use the newer style filter) instead of the 51626 wix number
the oil pressure switch on the newer ones have a slightly different connector but the thread pattern is the same as the old. i have an 88 block in my 92 4.0HO and no problems at all. you should have no problems using the later model block in a non HO motor, hope the build up goes well
 
Arakele --

Did you use the newer head and manifolds, or did you use only the newer block, with the Renix head and manifolds?

Just want to keep us all on the same page.
 
i re-used the 92 head and intake and put it on a 88 block with all 88 internals. and since i could go back in years im assuming he can go forward and use a 91 block on a 90.
 
Did you use the '88 throttle body or the '92 throttle body? If you used the '88 TB, how did you adapt it to the '92 intake manifold?
 
the only thing i used from the 88 engine was the block and engine internals,

also i had to make a bracket for the newer coil location, i mounted it to one of the bolts on the valve cover, the older blocks dont have the hole for the coil bracket. but since his is older he shouldnt have to worry about that either
 
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